The present invention relates to a semiconductor device for power conversion, such as a VVVF inverter.
A structure of a semiconductor apparatus according to the prior art is shown in FIGS. 3(a) and 3(b), and an inverter circuit of the semiconductor device is shown in FIG. 4. In FIGS. 3(a) and 3(b), reference numeral 1 designates a package for forming the device in a rectangular shape; 2 and 3 designate positive and negative DC input terminals (P, N); 4 designates AC output terminals (U, V, W); and 5 designates a control terminal of a semiconductor chip, such as IGBT, mounted in the package 1. The terminals 2, 3, 4 and 5 are arranged on the upper surface of the package 1, as illustrated in FIGS. 3(a) and 3(b).
Inside the package 1, six pairs of semiconductor chips are mounted as shown in FIG. 4 to form a three phase bridge circuit, wherein an IGBT (insulated gate bipolar transistor) 6 as a semiconductor chip for switching and a free wheeling diode 7 are coupled together. In FIG. 4, reference numeral 8 designates a rectifier circuit of a DC power supply, and 9 designates a motor which is connected to the AC output and controlled to variable speed.
In the above structure, the speed of the motor 9 is adjusted by variably controlling the voltage and the frequency of the AC output from the AC output terminals 4 while the IGBTs 6 are switched on and off at an appropriate timing.
In this case, a main circuit current flows from the DC side to the AC side via the IGBTs 6 or from the AC side to the DC side via the IGBTs 6 and the free wheeling diodes 7 by the switching operation of the IGBTs 6. However, since the current variation rate di/dt is high at the time of high speed switching of the IGBTs 6, stray inductance 10 (inductance value L) of internal wiring on the DC side causes surge voltage L.times.di/dt. The surge voltage is added to the DC input voltage and is supplied to the IGBTs 6 and the free wheeling diodes 7, so that the constituent elements of the chips break down when the surge voltage exceeds the withstanding voltage of the chips. To solve this problem, snubber capacitors 11 for surge suppression are connected between the positive and negative DC input terminals 2 and 3, as shown in FIG. 4 to suppress the surge voltage caused by the stray inductance 10 of the internal wiring.
In the surge voltage protection circuit shown in FIG. 4, the snubber capacitor 11 connected between a pair of the DC input terminals 2, 3 on the far side (right side in FIG. 4) from the DC power supply shows less surge suppression than that of the capacitor 11 connected between a pair of the DC input terminals 2, 3 on the near side to the DC power supply. This problem is solved by connecting conductor bars 12 as shown in dotted lines in FIG. 4 such that one conductor bar 12 connects the positive terminals with each other and the other conductor bar 12 connects the negative terminals with each other. In this structure, the current in the DC side main circuit is divided into two paths including the conductor bars 12, so that surge voltage is suppressed more effectively.
If the above described internal arrangement is adapted to the semiconductor apparatus of FIG. 3, the bars 12 externally connected between the DC input terminals 3 can not be wired in the shortest straight distance, because the AC output terminals 4 between the DC input terminals 3 and insulative partition walls 13 disposed between the terminals obstruct straight wiring of the conductor bars 12. Thus, the conductor bars have to be made long, which increases inductance component and deteriorates surge suppression effect of the snubber capacitors 11. This problem is more serious in a larger package for a semiconductor device with a larger current capacity, because the internal wiring is longer.
In view of the foregoing, the invention has been made, and an object of the invention is to provide a semiconductor device, wherein a plurality of switching conductor chips coupled with free wheeling diode chips is arranged in a bridge circuit and installed in a package, the semiconductor device providing an especially effective terminal arrangement for suppressing the surge voltage caused by the stray inductance of the internal wiring by the combination of the snubber capacitors and the conductor bars connected between the same polar terminals in the DC input terminals.